Hermione Granger.
Brightest witch of her age
Polaris is in the constellation Small Bear (Ursa Minor). I didn't check whether it actually is the brightest star in that constellation.
The feminine gender of witch is witch. Both male and female practitioners are commonly referred to as witches.
The key characters in "The Lion, the Witch and the Wardrobe" by C.S. Lewis are the Pevensie siblings: Peter, Susan, Edmund, and Lucy. Aslan the lion and the White Witch are also central characters in the story.
Witch Boards are also referred to as Ouija Boards. Yes, they are real.
There is no scientific name for a witch as witches are fictional characters in folklore and mythology.
Sorceress or Enchantress would probably be appropriate.
In the Vedic Age, a witch was called a Yogin. Nowadays witches are referred to as Daayan or chudail.
Rapunzel, the Prince, and the evil witch
The main characters in "The White Witch of Rosehall" are Annie Palmer, the infamous white witch of Rose Hall in Jamaica, and Robert Rutherford, an Englishman who becomes entangled in Annie's dark world. Other characters include slaves at the Rose Hall plantation and various supernatural entities.
Smurfette in costume. Gargamel was also referred to as a Wizard.